360 Piston Depth

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moparlewellen

moparlewellen

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Hey all, I got a 360 for my 71 dart at a machine shop here in town. $600 got me the block bored .030 over, crank, rods with new speed pro cast pistons installed, and the rest of the rebuild kit.

I got the whole bottom end together and I went to measure the piston depth, had to use my dial caliper, but its .130" in the hole! Is this right? That would mean with the dished pistons and a 64cc chamber I would only get 8.15:1 compression....Would it be more cost efficient to get different pistons or mill the head/block deck to get to 9.5:1?

I also have a set of early 318 heads with a closed chamber, could those be ported and put bigger valves in them to get them on my 360? I would like to turn 6000 rpm with ease. Or should I spend the cash and buy some new cast indy heads.
 
Summit has speed pro h116cp30 . I believe these are duplicate weight. Should bring your piston depth to around .020 down. Ask a tech guy at summit about the weight. I believe stock piston is around 584 without the pin. about 738 with.
 
If you have a 64 cc chamber you will be about what you said for compression. That is too low. Get the correct Pistons and get the CR up in the 9.5-9.7:1 area. Cam accordingly.
 
Defiantly bite the bullet and change pistons. Youl be doing a lot of milling to get the c.r up that far. Then, shimming rockers,or adjustable rockers or,push rods.Those Indy cast iron rebuilt heads get a big thumbs up from me! $550 got a new looking set of 75 360 castings, 3 angle valve job, all new stainless valves with 2.02 intakes,resurfaced, 509" springs, chrome only retainers, bronze guides. Allihad to Do wasblend the bowls a little where they opened up the seat for the 2.02 valves. Even the valve guides were machined down nicely for hi lift cam. Very good heads for price!
 
stock 360 pistons are down around .100". cast replacements are "compensated" so are down around .120". what heads are U using ? Chrysler said 360 heads are 64cc but they are more like 70cc. you would need to cut the block heads around .100", not the best way to go. that is why we install 1 or 2 pistons and measure deck. I like the h116p
 
Marcohotrod said:
stock 360 pistons are down around .100". cast replacements are "compensated" so are down around .120". what heads are U using ? Chrysler said 360 heads are 64cc but they are more like 70cc. you would need to cut the block heads around .100", not the best way to go. that is why we install 1 or 2 pistons and measure deck. I like the h116p
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Yup, I'm all for cutting the deck and getting the piston where it should be, but I just would not want to cut an 1/8 inch off the deck, when I can buy a better piston.
 
yellow rose said:
Yup, I'm all for cutting the deck and getting the piston where it should be, but I just would not want to cut an 1/8 inch off the deck, when I can buy a better piston.
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What's the scoop on the Sealed Power 405CP pistons? 140 Seems pretty cheap for hypereutectic pistons. Wondering if they'd make a good stock replacement piston in a mild 360 and if theft get the c.r up a little with stock block and unmilled heads
 
the 405cp is about .5 higher comp ratio than stock, with a compression distance of 1.637", and will have a deck height of about .055" and is a flattop with 4 valve reliefs
 
Thats what I figured, I found some kieth black pistons that are a little more than .100" taller than the ones I got for around $260. Those will bring me up to 10:1 with a .04 gasket, 5 cc piston dish and a 64 cc head.

Those indy heads will have to wait till tax return season....haha.

I did pick up a nice holley dominator intake from a pawn shop here. Spent $60 on it then took it to my machine shop to get put in the shot machine for an extra 10.
 
I have a 360 30 over with the 405CPs in it Hughes Whiplash cam plus matched springs, double rooler chain, X Heads, airgap manifold, just looking for a good cruiser, did not want to over do it, the block is 1975 still on the engine stand. Good luck on your build.
 
scott hoffman said:
I have a 360 30 over with the 405CPs in it Hughes Whiplash cam plus matched springs, double rooler chain, X Heads, airgap manifold, just looking for a good cruiser, did not want to over do it, the block is 1975 still on the engine stand. Good luck on your build.
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Any idea what your actual c.r came out being with the 405 pistons?
 
moparlewellen said:
Thats what I figured, I found some kieth black pistons that are a little more than .100" taller than the ones I got for around $260. Those will bring me up to 10:1 with a .04 gasket, 5 cc piston dish and a 64 cc head.
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Careful hoss..... those KB107's + pins weigh about 80 grams less per unit than the stock ones. So you would be making a weight change that needs a crank re-balance. I personally would do that to get better CR (which you can always adjust donw with thicker heads gaskets) and lower weight in the rotating assembly, but be sure you want to spend the extra $$.

If not, the H405CP's are an option; IIRC they weight the same as the stock units; you have to download the FME catalog to verify the weight. Using the .028" thick 1121G head gaskets would make up for a bit of CR loss; you would end up with about 9.25 SCR with that combo and 64 cc heads.
 
Dartish said:
Any idea what your actual c.r came out being with the 405 pistons?

the exact number no, but will not be much more than stock, as I was not trying to reinvent the wheel with this 360, got it for a very good price with a stock rebuild, changed out the pistons and cam and the Xheads are from a 340 stroker project on hold, The Hughes eng cam witch is the whiplash cam is designed for stock CP, as to not have to rebalance or change pistons, going into my suns 73 roadrunner who is 18 just enough power but not to much.
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Just wondering if those 405 pistons raised the comp much over a stock DISH piston since they have 4 big valve reliefs. Was hoping to get up around 9.1 with the 75 360 heads without doing much milling. Heads had 010" shaved off already
 
Guess I'll have to check out Hughes website. Are the "whiplash" cams a new line? When I built my 360 I was looking at Hughes for a good street can with plenty of vacuum and torque but the ones I was looking at had short duration like I wanted but wayyyyy more lift then I wanted to run with my stock stamped rockers. Saw a set of new stainless roller rockers,complete kit, for small mopars for $200. I bet those are some hi quality pieces.lol
 
I'm building a 1976 360 right now with h405cp pistons, 028 head gaskets and EQ closed chamber heads. Lunati 60402 cam and 1.6 roller rockers
It should be around 9.3 to 1 compression
 
I have a set of H405c .040 pistons...they weight 590 grams plus 154 for the pin
the H116 .030 weighted 580 plus 154 for the pin
 
I have a set in a 360. Cast crank, reconditioned rods, exhaust manifolds. 268 cam and an rpm intake are the only speed goodies on it. I cant make it ping on 87 at 8:1, and still lay 70 feet of rubber when I nail it. Not a bad street cruiser at all. Its no track car.
 
Dartish said:
Just wondering if those 405 pistons raised the comp much over a stock DISH piston since they have 4 big valve reliefs. Was hoping to get up around 9.1 with the 75 360 heads without doing much milling. Heads had 010" shaved off already
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The answer was posted for you above.
 
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